In case there’s any confusion, working 
out when you have tender muscles does not raise your risk of injury, according to research presented 
at the US National Strength and Conditioning Association conference last year. Highly resistance-trained weightlifters had their susceptibility to injury measured both before and two days after an intense lifting session. The result: they were no more likely to be hurt while lifting with sore muscles than without. Still, for best results, rest your muscles for at least 48 hours between workouts, because you need to Chill Out To Muscle Up.